PROJECT SUMMARY The medical and socioeconomic impact of subacute and chronic shoulder pain is high, resulting in 12 million visits to physicians and over $7 billion in direct costs in the United States. The most common cause is subacromial impingement syndrome (SIS), which accounts for 30% of all shoulder pain. Approximately 35% of those who present with SIS are refractory to conservative management. For those who have failed conservative management, there are no established treatments to reduce their pain. Our long-term goal is to develop a therapeutic intervention to reduce pain related to SIS. We completed a pilot trial of 3-week percutaneous peripheral nerve stimulation (PNS) for those with chronic shoulder pain due to SIS that was refractory to conservative treatment that showed 60% of subjects had successful treatment of pain that lasted at least 3 months. A multimodal treatment with different mechanisms of action may be more efficacious than a unimodal treatment. The primary objective of this 2 site RCT is to determine the efficacy of multimodal treatment of percutaneous PNS combined with PT in reducing shoulder pain secondary to SIS refractory to conservative management compared with the unimodal treatment of shamPNS + PT. The secondary objectives of this multisite RCT is to explore mechanisms of PNS for the treatment of SIS, and to determine which characteristics can predict successful treatment with PNS or PT. In order to accomplish these objectives, the investigators designed a multi-site, placebo controlled, double-blinded RCT to compare the efficacy of PNS+PT to shamPNS+PT. Measures of pain, pain interference with ADLs, capacity for ADLs, QoL, shoulder biomechanics (shoulder abduction strength, shoulder range of motion), and measures of central sensitization (pain thresholds, secondary hyperalgesia, and temporal summation) will be measured. Participants will be followed for a total of 24 weeks after treatment has concluded.